[2.0b5] installing maas-region-api and maas-dns should only configure bind when connected to the db

[Andres Rodriguez]

When installing MAAS (maas-region-api/maas-dns) it configures some bind files in order to ensure MAAS can work with bind. However, instead of doing this in packaging by calling scripts, this should be done automatically by MAAS when connecting to the DB.

The reason for this is that when you install maas-region-api and maas-dns on its down for HA< users will have to run bind configuration commands manually.